TECHNICAL PUBLICATIONS:

Printed polymer transistor arrays for displays and imaging

IMAPS 2003

Organic semiconductors are attractive materials for the fabrication of transistor arrays in device applications such as inexpensive, large area displays and image sensors and smartcards. Polymer semiconductors offer solution processing at low temperatures, on flexible substrates, and potentially at low cost. While spin-casting of the solutions is suitable for research, patterning of the active material decreases device-to-device leakage, improving device characteristics. Direct patterning of active materials by inkjet printing or other fluidic processing techniques, explored by several groups, minimizes both the number of processing steps and the use of materials, and therefore lowers the cost of device fabrication and improves manufacturability. Direct writing of mask material for definition of contacts is also a simple and inexpensive patterning process for building device arrays. We have developed methods to fabricate arrays of organic transistors (OTFTs) using direct printing to completely replace photolithography. In this multiple-mask process, metal for the source/drain contacts and the gate are patterned using jet-printed wax as a resist for wet etching, and the organic semiconducting polymer is deposited using inkjet printing and other fluidic deposition processes. We describe the processing approaches and compare alternative techniques to pattern the semiconductor. Characterization of our printed organic transistors shows field effect mobility and on/off ratios that compare favorably with OTFTs fabricated by spin-coating on control substrates.